1. Field of the Invention
The invention relates to a vehicle transmission, and particularly to a dual-drive transmission.
2. Description of the Related Art
The need for a transmission in an automobile is a consequence of the characteristics of the internal combustion engine. Engines typically operate over a range of 600 to about 7000 revolutions per minute, while the car's wheels rotate between 0 rpm and around 1800 rpm.
Furthermore, the engine provides its highest torque outputs approximately in the middle of its range, while often the greatest torque is required when the vehicle is moving from rest or traveling slowly. Therefore, a system that transforms the engine's output so that it can supply high torque at low speeds, but also operate at highway speeds with the motor still operating within its limits, is required. Transmissions perform this transformation.
As vehicles travel downhill, they usually coast, i.e., their engines are in gear and operate at idle speeds to reduce fuel consumption yet at the same time controlling vehicle velocity. However, resistance generated by the engines operating at idle speeds also significantly affects the coasting distance. In addition, as the engine operates at idle speeds, the speed of the vehicle cannot be controlled by the engine, and in essence the transmission is “single drive”.
CN Patent 2224116 discloses an axle shaft clutch for a driving wheel, which implements centrifugal separation during high-speed traveling of vehicles, so as to increase coasting distance after an engine retards the throttle. However, disadvantages of the axle shaft clutch include the following:                1. Centrifugal separation cannot be implemented at low-speeds, and thus coasting distance is not increased at low speeds;        2. The traveling speed cannot be controlled as the vehicle coasts downhill and the engine operates at an idle speed, and thus security is not ensured; and        3. The axle shaft clutch operating in a free state at a critical speed affects stability of the vehicle and increases operating noise.        